A known technique relating to an air conditioning system including an air conditioner and a ventilator to operate in an interlocking manner is described in Patent Document 1, for example.
According to this technique, the ventilator performs ventilation while the air conditioner implements heating operation. The ventilator exceptionally stops ventilation during defrosting operation if the air conditioner implements defrosting operation during the heating operation. Specifically, implementing the defrosting operation practically means implementing cooling operation to reduce a room temperature. Performing ventilation in this circumstance cools indoor air further to increase a heating load on the air conditioner that is imposed after the defrosting operation. As a result, indoor space is not heated efficiently after the defrosting operation, and it takes a long time for the indoor space to reach a set temperature. For this reason, the ventilator stops ventilation during the defrosting operation.
However, during heating operation, the air conditioner may implement an operation of practically cooling the indoor air or an operation of not heating indoor air as well as the defrosting operation. Examples of such operations not intended for temperature control include an oil recovering operation of recovering a lubricant and a heating thermostat off operation implemented by turning a thermostat off. However, simply stopping ventilation in these operations as well as in the defrosting operation is assumed to cause insufficient ventilation of indoor space.